The 2nd sentence feels like an implied question e.g. "Surely, [he] is kin of a frog or something." (implying that the speaker suspects the nighthawk isn't the kin of a frog, but something else entirely")

But (as far as I know) a sentence that ends in だよ is always declarative unless a "question word" is included. e.g. "Surely, [he] is kin of a frog or something." (The speaker has no suspicions. It's simply a matter of fact that the nighthawk is the kin of either "a frog" or "something").

Now since the expression 何か uses the 何 kanji (which is also used in other interrogative words, like "what") I wondered if 何か in this context could function as a "question word" and carry a questioning tone. e.g. "I am going to do something?"

Another example of the 1st tone: "My dog is a hound... or something...." (this sentence isn't technically a question, but it's still implying a question of authenticity and a suspicion that the dog isn't really a hound)

Another example of the 2nd tone: "My dog is a hound, or something."(there are no implications in this sentence. It's just a simple matter of fact the dog is either a hound or something else.)

I think you have done most of the work here already, but there are some confusing parts of your question. The speaker is certain that it's either related to frogs "or something". That said, you might want to elaborate on what you mean by "question word". I don't believe 何か is an interrogative word, if that's what you mean to ask. Also, while both Japanese and and English can use constructions like "or something" to express doubt (as you have shown), doubt != an implied question.
– MindfulFeb 19 '18 at 1:14

Yea, I meant interrogative words. e.g. "What", "who", etc. My fuzzy understanding of Japanese is that some forms of interrogative words can be used in declarative sentences to imply a question about something. Since 何 is the kanji for "what" I was thinking 何か might carry a questioning tone to it. e.g. "There's Something About Mary." = "There's What Thing About Mary?" guidetojapanese.org/learn/complete/questionwords
– HyperglyphFeb 19 '18 at 2:01

1 Answer
1

何か here is not a question word. (「何 + か」 can be a question word in different structures.)
[何]{なに}か here means "something".
「～か何か」 = "~~ or something similar" "~~ or something like that"
(The か in 親類か is a parallel marker / 並立助詞.)

implying that the speaker suspects the nighthawk isn't the kin of a frog, but something else entirely

The sentence means that the speaker suspects the nighthawk is the kin of a frog or something (like a frog / similar to a frog).

Does Japanese even have implied questions (and doubt) like English does?

After reading your comment below ("I'm sure he's a frog's cousin or something." could indicate doubt or a question of authenticity. i.e. You don't really think he's a frog's cousin, you think he's something else.), I can't think of a way to directly translate/convey the sentence/meaning into Japanese (without sounding really translated, at least.)

What's the best translation of that 2nd sentence?

きっと、かえるの親類か何かなんだよ。
"I'm sure it/he's a frog/toad's cousin or something (similar / like that / of that kind)."
"It/He must be a frog/toad's relative or something (similar / like that / of that kind)."

(I don't know if this is the best translation, but it's what it means. Please modify it to what sounds natural in your language.)

Ah, so it's 蛙 and not 孵る. As usual, this children's book is using kana for a lot of words that are normally written with kanji. So I just assumed it was "to hatch" as that related to birds.
– HyperglyphFeb 19 '18 at 1:42

As for examples, I mean (in English) the sentence "I'm sure he's a frog's cousin or something." could indicate doubt or a question of authenticity. i.e. You don't really think he's a frog's cousin, you think he's something else. But, if the same sentence is read without inflection, e.g. "I'm sure he's a frog's cousin or something." Then it's just a simple statement of fact. You're sure he's a frog's cousin, or something like that.
– HyperglyphFeb 19 '18 at 1:53

Keep in mind that I originally thought it was "to hatch" not "frog". So, my reading was "Surely, he hatched of birds or something." (implying a question of whether the Nighthawk was really a bird, because he was so ugly).
– HyperglyphFeb 19 '18 at 1:53

I edited the original post with examples and your corrected translation. Hopefully, it's much clearer now.
– HyperglyphFeb 19 '18 at 2:46